1. Field of the Invention
This invention relates to a method and apparatus for removing excess moisture from moisture condensing surfaces. More particularly, this invention relates to a method and apparatus for removing excess moisture from the evaporator coils employed in air-conditioning systems.
2. Description of Related Art
Air-conditioning systems generally comprise five mechanical components: a compressor, a fan, a condenser coil, an evaporator coil, and a refrigerant. Air-conditioning systems transfer heat from the inside of a space to be conditioned to the outside. Refrigerant in the system absorbs the excess heat and is pumped through a closed system of piping to an outside coil. A fan blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air. Because the heat is removed from the indoor air, the space to be conditioned is cooled.
Two types of heat are removed by air-conditioning systems: temperature-associated sensible heat and moisture-associated latent heat. An evaporator coil typically operates by performing about 25% moisture removal and 75% cooling. If the sensible-heat ratio falls below 75%, then overcooling occurs in meeting the moisture-removal demand. This unnecessary cooling is usually rectified by adding heat to the space, consuming even more energy. Latent-heat ratios often become higher than 25% in hot and humid climates, where fresh air introduction brings in significant levels of moisture, upsetting the temperature and moisture balance of interior spaces and reducing comfort levels. Excessive moisture in the air may also contribute to indoor air quality problems.
Over the past several years, manufacturers have been working to increase the efficiency of residential and commercial air-conditioning systems. One method of increasing the air conditioner system efficiency has been to reduce the spacing of the fins on the evaporator coil. However, the result of this increase in the number of fins present is that moisture that is removed from the indoor air as it passes over the coil is retained on the coil instead of flowing down the drain.
Numerous articles have been published over the past several years discussing the issues related to retained moisture on high-efficiency air-conditioning coils. See, for example, Harriman III, L. G. et al., “Dehumidification Equipment Advances,” ASHRAE Journal, August 2002, pp. 22-27; and Shirey III, D. B. et al., “Dehumidification at Part Load,” ASHRAE Journal, April 2004, pp. 42-47. In addition, there is concern that the moisture in ductwork provides a breeding ground for bacteria. The situation is exacerbated by operation of the air-conditioning system in a continuous fan mode to allow air cleaning systems to perform. In such cases, as the air conditioner operates in a cycling fashion, the system loads retained moisture onto the evaporator coil, and then when the air conditioner cycles off, the fan evaporates the moisture and blows it into the conditioned space. This is an energy benefit from a sensible consideration as the evaporation lowers the air temperature, but if the space already has too much moisture, it can make the space uncomfortable. Additionally, the presence of excess moisture in both the ductwork and the conditioned space can have negative consequences.